ASTM D664-24 PDF

Full title and description

Standard Test Method for Acid Number of Petroleum Products by Potentiometric Titration — ASTM D664-24. This ASTM test method defines procedures for determining the acid number (total acid number, TAN) of petroleum products, lubricants, biodiesel and biodiesel blends using potentiometric (non‑aqueous) titration techniques; it includes guidance for sample preparation, reagents, electrode use, manual and automated titration, and reporting of results.

Abstract

ASTM D664-24 specifies two test method variants (Test Method A for petroleum products and lubricants soluble in toluene/isopropanol solvent mixtures; Test Method B developed specifically for biodiesel and biodiesel blends with low acidity) and describes potentiometric titration with potassium hydroxide in isopropanol to report acid number in mg KOH/g. The method is intended for quality control and in-service monitoring but is not a direct predictor of corrosion or performance in service. The 2024 revision updates format and references and replaces the previous 2018 edition.

General information

• Status: Active standard (current, in force).
• Publication date: May 1, 2024 (ASTM D664-24).
• Publisher: ASTM International.
• ICS / categories: 75.080 (Petroleum products in general).
• Edition / version: D664-24 (2024 revision; replaces D664-18E2).
• Number of pages: 12 pages (standard document length for D664-24).

Key bibliographic identifiers: DOI 10.1520/D0664-24; developed by ASTM Committee D02 (Petroleum Products, Liquid Fuels, and Lubricants).

Scope

This test method covers procedures for determination of acidic constituents in petroleum products, lubricants, biodiesel, and blends of biodiesel that are soluble (or nearly soluble) in the specified solvent systems. Test Method A is intended for conventional petroleum products and lubricants soluble in toluene/isopropanol mixtures and covers acids with dissociation constants greater than about 10⁻⁹ (precision statement range noted for typical materials). Test Method B is designed for biodiesel/biodiesel blends with low acidity and requires an automatic titrator with endpoint-detection capability. The standard notes that extremely weak acids and some salts may not be measured and that values may not be numerically equivalent to results from other acid‑value methods; for crudes and very heavy or waxy materials, ASTM Test Method D8045 is recommended.

Key topics and requirements

• Principle: potentiometric (non‑aqueous) titration of a dissolved sample with KOH (in isopropanol) while monitoring electrode potential to detect the end point.
• Test Method A vs B: Method A for petroleum/lubricants soluble in toluene/isopropanol; Method B for biodiesel and low‑acidity blends (automated titrator required).
• Solvents and reagents: commonly toluene and isopropanol (propan-2-ol) solvent mixtures and standardized KOH titrant in isopropanol.
• Electrodes and instrumentation: proper selection, conditioning, and calibration of reference and indicator electrodes; options for manual endpoint determination (inflection/derivative plotting) or automated endpoint finding.
• Precision and range: precision statements are provided for specified acid‑number ranges relevant to typical lubricants and biodiesel samples; users should consult the precision section for numerical repeatability and reproducibility limits.
• Reporting: acid number expressed as mg KOH per g sample (TAN); note on optional reporting of strong acid number (SAN) where appropriate.
• Limitations and safety: method does not predict corrosiveness; users must manage solvent hazards and follow laboratory safety practices and regulatory limits.

Typical use and users

ASTM D664-24 is used by lubricant and fuel formulators, quality control laboratories, in‑service oil analysis laboratories, biodiesel producers, research laboratories, petrochemical laboratories, and certification bodies to quantify acidic constituents (TAN) for formulation control, stability/degradation monitoring, and batch release testing. It is commonly incorporated into oil analysis programs for equipment maintenance and failure diagnostics.

Related standards

Commonly referenced and related methods include: ASTM D974 (acid or base number by color‑indicator titration), ASTM D3339 (related titrimetric procedures), ASTM D8045 (acid number for crude oils and heavy fractions by catalytic/thermometric titration), ISO 6618 / ISO 6619 (colour‑indicator and potentiometric neutralization/acid number methods), and EN/DIN standards such as EN 12634 (non‑aqueous potentiometric titration for lubricants). Users should select the method suited to sample type and regulatory/contractual requirements.

Keywords

acid number, TAN, total acid number, potentiometric titration, non‑aqueous titration, KOH titrant, lubricants, biodiesel, Test Method A, Test Method B, SAN, ASTM D664-24.

FAQ

Q: What is this standard?

A: ASTM D664-24 is the 2024 ASTM test method that specifies potentiometric titration procedures to determine the acid number (mg KOH/g) of petroleum products, lubricants, biodiesel and blends.

Q: What does it cover?

A: It covers sample dissolution, reagents, electrode selection and conditioning, titration procedure (manual and automated), calculation and reporting of acid number, and method limitations; two method variants (A and B) address conventional lubricants and biodiesel blends respectively.

Q: Who typically uses it?

A: QC laboratories in petrochemical and lubricant manufacturing, in‑service oil analysis labs, biodiesel producers, research labs, and maintenance/diagnostic services use D664 for product control and monitoring of oxidation or additive depletion.

Q: Is it current or superseded?

A: D664-24 is the current active edition published in 2024; it supersedes the earlier 2018 revision (D664-18E2). Check your organization's standards subscription for the latest confirmation if required.

Q: Is it part of a series?

A: It sits among a family of acidity/neutralization test methods (ASTM D974, D3339, D8045 and related ISO/EN standards) that address acid/base measurement for different sample types and detection techniques. Selection depends on sample matrix and intended use.

Q: What are the key keywords?

A: Acid number, TAN, potentiometric titration, KOH, biodiesel, lubricants, non‑aqueous titration, SAN, ASTM D664-24.